Programmable position controllers, such as robots, have proven very useful in performing routine and repetitive tasks in the manufacturing area. One such task is the deburring of the edges of machined, metallic objects. A robotic arm may be fitted with a deburring tool and programmed to follow a path around the edge of the metallic object which is to be deburred. An improvement in quality and consistency of the deburring process may result from the use of a robotic deburring.
There are, however, difficulties associated with the use of robotically controlled deburring tools. Since the programmed path of the robotic arm is in essence a series of incremental steps, there are errors in the path of the robotically controlled deburring tool relative to the surface to be machined. In addition, the surface itself may have cavities within and/or protrusions extending from it. These pockets and protrusions interfere with the path and cutting force of the robotic tool. A protrusion will urge the cutting surface of the deburring tool out of its path and cause a consequent increase in cutting force. The increased cutting force may cause and the cutting surface to cut too far into the surface. Additionally, the increased cutting force may cause damage to the cutting surface of the tool. A cavity may cause the deburring tool to separate or diverge from the surface to be machined. The separation of the cutting surface of the tool from the machined surface will prevent the deburring of that portion of the machined surface from being accomplished. The quality of the deburring and of the product being produced will thereby suffer.
A well known solution to the inaccuracy in the programmed path and to the surface variations is to build compliance into the robotic arm. Compliance compensates for errors in the path and variations in the surface by permitting limited movement of the tool while maintaining an acceptable cutting force. In this way, variations in the surface or inaccuracies in the programmed path which are within the limits of the compliance will be accommodated and damage to the cutting surface and the finished product may be minimized.
Several types of compliant tool holders have been disclosed in the prior art. In U.S. Pat. No. 4,637,775, issued to Hisso Kato, entitled "Industrial Robot Device", compliance is provided by a spring built into the device holding the tool. The spring permits the tool, which is comprised of the cutting surface and the drive means for the cutting surface, to move laterally, relative to the axis of the tool, away from the edge. In U.S. Pat. No. 4,860,500, issued to Robert Thompson, entitled "Passive Actuator To Maintain A Constant Normal Cutting Force During Robotic Deburring", an air cylinder with a low friction piston is used to provide a zero spring rate compliance. As with Kato, the cutting surface and the drive means of the tool are permitted to move laterally to accommodate path errors and surface variations. A drawback to both types of lateral compliance is that in precision machining there may not be room to permit sideways compliance. For instance, structure adjacent to the edge being deburred may preclude the use of a sideways compliant tool holder. In addition, the sensitivity of the compliance mechanisms has been insufficient for intricate patterns of machining. The weight associated with the prior art compliant tool holders has been too great to provide a tool holder which is responsive to changes in path or to variations in the machined surface. In effect, the momentum of the compliant tool holders results in additional cutting surface path variations.
The above art notwithstanding, scientists and engineers under the direction of Applicant's Assignee are working to develop compliant robotic tool holders.